1. Field of the Invention
The present invention relates to holders for cutting bits used on mining machinery and, in particular, to miner bit holders which include a bit holder attached to a rotating cutting drum and an indexible sleeve for receiving a rotatable cutting bit.
2. Description of the Invention Background
In the materials mining industry, as well as in other applications requiring the cutting of hard materials, it is typical to employ an apparatus which includes a vertically moveable rotating cutting drum which has cutting bits attached thereto. By virtue of the rotation of the cutting drum and the movement of the apparatus into the material to be cut the material is removed for further processing.
It is well known that such cutting bits and their holders are subjected to considerable stresses during the mining operation. Such stresses occur axially, vertically and transverse relative to the cutting bit. Accordingly, in normal mining operations, cutting bits require frequent replacement due to wear or breakage. In fact, cutting bits must often be replaced on a daily basis. In view of these conditions, much effort has heretofore been directed to the provision of readily replaceable cutting bits which may be removed with a minimum of effort from their supports.
Because the bit holding devices are not the primary vehicles by which material is removed from the mine face, the bit holding devices are generally characterized by a longer service life. As such, bit holding systems have been developed which include a bit holder which physically retains the cutting bit and which may be mounted on the miner's cutting drum. Nevertheless, the bit holders themselves are subject to considerable wear and breakage and may require replacement on two to six month intervals.
Replacement of the bit holder can result in considerable expense and down time for the mining machinery. Therefore, bit holding devices have been developed which include a replaceable sleeve disposed between the bit holder and the cutting bit. The use of these sleeves extends the life of the bit holders by limiting the wear to which the bit holder is subjected. In the past, sleeves have been either freely rotatable within the bit holder, or they have been fixed in one position relative to the bit holder depending upon the application. The sleeve of the rotatable type has a longer service life due to even wearing on surfaces which contact the mine face. However, rotatable sleeves wear the bit holders in which they rotate. Therefore, with mining bit holders in the past, one had to make a choice between rotatable sleeves which, although they enjoy a long service life, cause excessive wear of the bit holder, and non-rotatable sleeves, which do not wear the bit holder as quickly, but must be replaced more often due to their wearing.
Reference is made to my copending application Ser. No. 578,908, filed on the same date as the present application, entitled "Apparatus for Holding a Cutting Bit", which is directed to analogous concerns as this application and whose disclosure is hereby incorporated herein by reference.
Therefore, the need exists for a non-rotatable sleeve which will not cause excessive wear of the bit holder but which can be rotated manually and fixed in one of a number of positions to extend its service life.